Mr. Hayden added that Mr. Mehsud is receiving support from Al Qaeda, an accusation also asserted by the Pakistani government. The alliance between Mehsud and Al Qaeda, Hayden says, presents a new threat to Pakistan's stability.

The Los Angeles Times cites similar comments from a US intelligence official who, speaking anonymously, said, "There is certainly no reason to doubt that [Mehsud] was behind this." Like Hayden, the official did not disclose how the CIA came to such a conclusion. The Times notes that Pakistani officials, including Mr. Musharraf, accused Mehsud largely on the basis of a telephone-call recording in which a man they believe to be Mehsud congratulates a cleric for his followers' success in killing Bhutto. Mehsud has denied involvement in Bhutto's assassination, but he has not yet commented on the recording.

The Times adds that an official in Bhutto's Pakistan People's Party remained skeptical of the CIA's assertions, noting that the agency was unable to examine much of the forensic evidence because both the crime scene and Bhutto's vehicle were "hosed down" shortly after the attack.

The BBC adds that Mehsud is believed to lead some 20,000 insurgents, the majority of whom belong to the Mehsud tribe, and that Mehsud serves under Taliban commander Jalaluddin Haqqani, who allegedly aided Osama Bin Laden's escape from the Afghan mountain fortress in Tora Bora in 2002.

The US's conclusion that Mehsud was involved in Bhutto's murder echoes that of Scotland Yard, which Musharraf asked to investigate the assassination. The Sunday Times of London wrote last weekend that Scotland Yard found the evidence supported Musharraf's claim that Mehsud was involved.

The Times adds, however, that Bhutto's widower, Asif Ali Zardari, rejected Scotland Yard's findings and called for an independent, UN-led investigation into her death.